•Variation of polymerization, temperature, quality and source of iron precursors leads to the difference in ORR activity.•The relationship between the structure and performance is established by using advanced characterization methods.•Make it clear that iron, nitrogen, and carbon play the different role on ORR activity in the acid solution respectively.

Non-precious metal catalysts as the electrocatalysts for oxygen reduction reaction (ORR) attract great attention due to their activity and stability close to Pt/C. Herein, the iron-based catalysts for ORR are synthesized through the heat treatment of o,m,p-phenylenediamine/iron/carbon precursors. Variation of polymerization, heat-treatment temperature, quantity and source of iron precursors during the synthesis of the catalyst leads to the difference in ORR activity. A relationship between the structure and performance is established through the systematic investigation of synthesis–structure–performance in these catalysts by using advanced characterization methods. It is confirmed that iron, nitrogen, and carbon play different roles in ORR activity, respectively. The formation and amount of FeN complex, which are often proposed to be active sites for ORR, are consistent with species and environment of nitrogen and iron.